nillviod

My exhaust isn't giving off a steady hum and its starting to get to me. I get a mix between a "putt putt" sound and a thud like sound every few seconds coming out of the exhaust when idle... opposd to a steady hum.

Also, when I start the car up (this just started since it got cold) ... there is this fast, almost plastic sounding, vibration coming from either inside the car or right under the hood near the window. I have a feeling its inside the car but I'm not sure..

I know you guys are probably getting sick of answering questions about my car :p.. but I've just got a few left. These are all just noises and things I notice while running the car, and I'll soon run out of new things to pick up on. Thanks for the help.

-nill

911GT2

The "putt putt" sound is actually backfiring, surpressed by your cat. It is indicative of a rich (i.e. rotary friendly) idle. I had a bit of that before my Power FC was tuned, and I still get a little "putt" every now and then at idle. Nothing to worry about, just a rotary thing.

Not sure about the other vibration...?

racerfoo

i have those same issues. the idle is normal...you'll hear all kinds of interesting pops and stuff during idle. even with the stock exhaust, i would get a little pop noise every once in a while.

the vibration rattle noise i havnt solved. maybe the throttle cable loose, that what i think mine is, my friends mustang has the same problem.

rynberg

Does the "plastic" sounding rattle seem to be coming from behind the gauge cluster? Does it only happen when you are at idle and disappears the moment you start giving it throttle? If so, you are likely experiencing the not-so-infamous brake booster rattle.

Read this (originally posted by Ech - thanks):
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The TSB adds a rubber isolator to the mounting point that holds the brake booster line. You can't keep the valve from fluttering/ticking, but the isolator does a good job of removing the noise from the cabin. For $5-$15 and a few minuts, it is a good thing to do.

TSB 011/97.

F285-13-363 - Rubber Mounting - about $11 (a "stud") - this is the only part you have to order from Mazda
9994-00-600 - Flange Nut - about $2 - yes, for a single brass 10mm nut! A good place to save $2, if you don't mind a trip to the hardware store, or rummaging through that big bin of spare hardware you have.

Install (5 mins)
Need a 10mm socket, and crescent wrench (not sure of size)
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there is a metal vacuum pipe that runs along the top of the firewall. It is held on with two stamped metal brackets. The passenger end bracket has the engine ground on it. Both ends have easy access. This is the metal tube that the brake booster line, with the shuttle valve in it, connects to.
1. Remove the 10mm bolt from the drivers side bracket - toss it, swallow it, or add it to the big bin of misc hardware you have. Er, don't actually swallow it.
2. Loosen the 10mm bolt on the passenger side.
3. Screw the rubber isolator stud into the firewall where the driver's side bolt came from.
4. place the driver's side bracket on the other end of the stud
5. secure with the flange nut.
6. tighten the passenger side bolt again.
done.

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This solved the problem for very low cost on my car.

911GT2

Y'know it's funny. I never really noticed it before, but tonight when I got in my car I noticed the plastic noise. It definitely sounds like its coming from right behind the gauge cluster as rynberg suggested. I thought it was the defroster vents at first, but I held them down with my hand and the noise persisted.

Thanks for the info though rynberg, I'll have to check that out.

nillviod

Yeah I also listened really carefully and noticed that it only happens when I take my foot completely off the throttle. The second my foot touches the pedal though it will go away. Thanks for the info ill look into it as well

rynberg

911GT2 and Nilviod: I gaurantee that it's the brake booster. Well, ok, 95% sure...

In any case, if it doesn't fix it, you're out less than $10 and 2 minutes of time.